1. Field of the Invention
The present invention relates to indicators and more particularly to decay indicators, degree of ripeness indicators (in fermentation processes), general elapsed time indicators and the like, which can be applied to objects which are perishable or subjected to other changes of state, to provide to the consumer, user, or any control person a visible display that the moment has arrived in which a change of state in the object, and in the case of the simple elapsed time, has taken place or is to be expected.
2. Description of Related Art
Such indicators have been known in various forms. An indicator in which a visible display is brought about by color or change of the indicator by reaction of chemical substances and with destruction first of a barrier separating chemical substances is the object of prior patent application P 39 07 683 of the applicant. In the prior application, two chemical compounds reacting with one other under visible color change are first impeded in the reaction by microencapsulation. If the barrier of the reactant formed by the microcapsules is then destroyed by action of mechanical pressure, the reaction can begin.
Numerous other indicators to display elapsed times and/or changes of state have also become known, which aim at a solution of the varied requirements of indicators for respective purposes.
DE-30 29 289 shows an aging indicator, which is to be applied, for example, to perishable foods and consists of at least one sealed container, which includes a single compartment and contains at least one fluid, which is able to travel or to diffuse outward as a function of time and temperature through at least one part of the container, and the aging of the related product is evaluated by determining the amount of fluid leaked from this container.
DE-PS 32 10 907 relates to an indicator, in which the time/temperature stress of objects is detected in a fluid medium by the extent of penetration of a solvent and to control the penetration depth to which gelling agents are added to the solids contained in a storage element. Between the storage element and the fluid substance, a barrier made from a film strip is present, however, and this film strip initially has to be removed.
DE-PS 37 17 025 shows a display device, in which an indicator compound contained in a storage chamber is brought into contact by a channel with an indicator strip by using outside pressure, and the discoloration of the indicator strip begins and continues over the entire strip and with continuous discoloration the end of the period is indicated. Between the storage antechamber and the display channel, a gate can be made which basically prevents penetration of the indicator compound into the display channel.